[MC] Handle malformed target-feature

Author: sweiglbosker

llvm/lib/MC/MCSubtargetInfo.cpp

@@ -59,9 +59,11 @@ void ClearImpliedBits(FeatureBitset &Bits, unsigned Value,
 
 static void ApplyFeatureFlag(FeatureBitset &Bits, StringRef Feature,
                              ArrayRef<SubtargetFeatureKV> FeatureTable) {
-  assert(SubtargetFeatures::hasFlag(Feature) &&
-         "Feature flags should start with '+' or '-'");
-
+  if (!SubtargetFeatures::hasFlag(Feature)) {
+    errs() << "feature flag '" << Feature
+           << "' must start with either '+' or '-' (ignoring feature)\n";
+    return;
+  }
   // Find feature in table.
   const SubtargetFeatureKV *FeatureEntry =
       Find(SubtargetFeatures::StripFlag(Feature), FeatureTable);

llvm/test/CodeGen/Generic/invalid-target-feature.ll

@@ -0,0 +1,9 @@
+; Check that we handle a malformed feature flag gracefully.
+
+; RUN: llc %s -o - 2>&1 | FileCheck %s
+
+; CHECK: feature flag 'foobar' must start with either '+' or '-' (ignoring feature)
+define void @f() "target-features"="foobar" {
+entry:
+  ret void
+}